1. Field of the Invention
This invention relates to mixers for mixing flowable materials, and more particularly to an improved coil impeller mixing device which is very effective and efficient in mixing flowable products including highly viscous liquids such as petroleum distillation sludges, tars and the like, as well as for blending solids such as powdered materials into liquids, reducing particle size in blends (through impact in the mixing process) and for the processing of products such as foods, paint, polymers, ceramics, cosmetics, drugs and other products.
2. Description of the Prior Art
Mixing operations are so well known and widely used that little consideration is given to the subject by the average individual. At the same time, effective and efficient mixing is critical in the production and/or use of numerous products. A very substantial mixing industry has developed involving both domestic and industrial mixing devices and operations, and mixers ranging from small "test tube" models to large industrial process mixers requiring 300 horsepower or more are commercially available. It has been estimated that the industry's total annual revenue in this country alone may be as much as 1.2 billion dollars.
Industrial mixers typically employ impellers in the form of propellers, pitched blades, Rushton blades, bottom scraper blades, or high speed dispersers, emulsifiers. It is also well known to employ an elongated coil impeller supported on the end of a shaft driven by a drill motor or the like, and a device of this type is disclosed in U.S. Pat. No. 5,037,210. In this prior art device, the coil is loosely mounted on a drive shaft to enable the longitudinal axis of the coil to be deflected at a substantial angle from a plane perpendicular to the drive shaft axis. This feature enables the coil to contact the bottom of a container, for example a paint can, along the full length of the coil even though the drive shaft is not held perpendicular to the can bottom.
U.S. Pat. No. 3,132,849 also discloses a stirrer, or mixer, including a coil scraping and stirring element adapted to contact the bottom of a container while being driven about an axis substantially perpendicular to the bottom of the container. This device is intended for use primarily to prevent food from sticking to the bottom of the container during cooking and it does not employ the pumping feature of a relatively high speed impeller for mixing or homogenizing the entire contents of the container.
While the mixer industry has developed mixing technologies adequate for most industrial or commercial mixing and blending operations, many of these devices are relatively cumbersome, inefficient, and maintenance intensive, and frequently do not reliably produce the high quality uniform product desired, or require excessive time for producing the desired mixing action.
The known mixers have not been considered adequate for some operations such as removing sludge settled on the bottom of the large petroleum tanks at refineries and it is currently necessary to put such tanks out of operations periodically to be cleaned by hand. Also, some of the known mixing devices are not energy efficient and are not readily adaptable to variable conditions such as product depth in the mixing container. Accordingly, it is a primary object of the present invention to provide an improved coil impeller mixing device which is highly efficient and effective in mixing flowable products.
Another object is to provide such a mixing device which produces a highly uniform mixed product.
Another object is to provide such a mixing device which is capable of mixing products having a wide range of viscosities.
Another object is to provide such a mixing device which is highly effective in disbursing dry or powder materials in a liquid.
Another object is to provide such a mixing device which can readily be adjusted for effectively mixing materials of various depths in a mixing container.
Another object is to provide such a mixing device which can efficiently reduce particle size (through impact within the mixing container) in the material being mixed.
Another object is to provide such a mixing device which can process large solid and semi-solid masses into a fluid form without damage to the device.